The present invention relates to a method of growing of Group III-V compound semiconductor crystal layers on a silicon substrate, particularly to a method of growing a layer of Group III-V compound semiconductor crystal, which can have good perfection and surface morphology.
Recently compound semiconductor devices, such as FETs, etc., using Group III-V compound semiconductor such as GaAs, etc., in place of silicon materials have been noted.
In the fabrication of compound semiconductor devices, generally compound semiconductor crystal layers are grown on compound semiconductor substrates. Recently crystal growing methods for growing crystal layers of Group III-V compound semiconductors, such as GaAs, on silicon substrates have been much studied and developed. Silicon substrates have low production costs, and large-diameter silicon substrates can be easily produced and have good strength. If the compound semiconductor layers can be formed on large-diameter silicon substrates, they will yield a large number of compound semiconductor devices.
For the growth of compound semiconductor crystal such as GaAs, on silicon substrates is required a method of growing compound semiconductor crystal layers on silicon substrates, which can form good Group IXI-V compound semiconductor crystal layers having good crystal perfection and surface morphology.
As a conventional method of growing Group III-V compound semiconductor crystals on silicon substrates is known a method in which a silicon substrate is heat-treated in an ambient atmosphere of a reducing gas and a source gas for Group V, subsequently a low-temperature grown layer of a Group III-V compound semiconductor is first formed at a low temperature on the silicon substrate, and then a layer of the Group III-V compound semiconductor is epitaxially grown on the low-temperature grown layer.
But in the conventional method, when a Group III-V compound semiconductor layer is grown on a silicon substrate offset from (100) plane in [011] direction, the longitudinal axes of the etch pits formed by KOH treatment of a grown compound semiconductor layer are normal to the offset direction. It is known from phenomena that in the case that the longitudinal axes of the etch pits in the compound semiconductor layer on the thus-offset silicon substrate are normal to the offset direction, the grown compound semiconductor layer is inferior in surface morphology and crystal perfection. Thus, the conventional method cannot produce compound semiconductor layers having good surface morphology and crystal perfection.
As a method for solving the problem of the above-described conventional method is proposed a method described in Japanese Patent Laid-Open Publication No. 175690/1990. In this method, after a substrate is heat-treated in a reducing gas, a source gas for Group V is for the first time introduced to form a low temperature grown layer of a III-V compound semiconductor at a low temperature, and then a layer of the III-V compound semiconductor epitaxially grown on the low-temperature grown layer.
In comparison with the conventional method, this method improves the crystal perfection of the grown compound semiconductor layers.
But the method described in Japanese Patent Laid-Open Publication No. 175690/1990 has the problem that although the crystal perfection of the grown compound semiconductor layers is improved, the surface of the silicon substrate is contaminated in the heat treatment in a reducing gas atmosphere before the low-temperature grown layer is formed, which results in inferior surface morphology of the grown compound semiconductor layer.
The above-described conventional methods for growing compound semiconductor crystal layers have the problems that a large number of pits are appear on the as-grown surface of the compound semiconductor epitaxial layer, and the surface is rough and not flat, and the growth at a high temperature decreases pits on the as-grown surface, but raises a carrier concentration.
An object of the present invention is to provide a method of growing a compound semiconductor layer which can form on a silicon substrate a Group III-V compound semiconductor layer having good crystal perfection and surface morphology.